This invention relates generally to optical communication networks.
Optical communication networks may be subject to dispersion, which is the dependence of the refractive index of a medium on the wavelength of light traveling through the medium. Thus, dispersion involves changing the light velocity inside the medium, depending on its wavelength.
An optical network's velocity dependence on wavelength results in pulse spread. Dispersion restricts the information carrying capacity of a waveguide since, the wider the pulse, the fewer pulses that can be accommodated per interval, resulting in a smaller bit rate.
Lattice filters may be used as dispersion-compensators. While lattice filters can, in principle, implement any transfer function without any insertion loss, the fact that they use many tunable 2×2 couplers in series leads to a high insertion loss in practical lattice filters.
As the transmission speed of telecommunication networks has steadily increased, compensating the chromatic dispersion that data signals experience during transmission through optical fibers and other optical components has become an increasingly important issue. Chromatic dispersion has a direct impact on how far signals can be transmitted without error, with transmission distance scaling inversely with the square of transmission bandwidth. It has long been recognized that there will be an increasingly strong need for devices that can flexibly and accurately compensate for this chromatic dispersion.
Thus, there is a need for better ways to compensate for dispersion.